Partial support is requested for the 1999 Gordon Research Conference Muscle: Contractile Proteins to bring together biophysicists, biochemists, cell biologists and physiologists to address the mechanism of contraction and its regulation. While the actin-myosin contractile system has even the most extensively studied, it is now well recognized that acto-mosin based systems have fundamental roles in many cellular activities ranging from organelle transport to cell division. The overall focus of the conference will be the Molecular basis of Muscle Contraction and its Regulation. There are two major aims. One is to discuss important recent developments in the field ranging from newly determined molecular structures to single molecule studies in solution and in fibers as they relate to the contractile mechanism. In addition, new methods that may be applied to analysis of muscle contraction will be introduced. In the past decade the availability of atomic resolution structures for actin and myosin, techniques for studying single molecules, improved EM imaging methods, and the opportunity to study genetically-modified molecules have revolutionized the stud of the contractile process The questions, models, and underlying assumptions, predate these newer developments. The second aim of the conference is to focus on the major questions , models and controversial issues in light of recent results in discussion-based workshops. The size of the Gordon Conference (a maximum of 150 participants) is ideal. There will be nine sessions. In eight, there will be a small number of formal presentations followed by a discussion workshop on critical issues relating to the session. The discussions will be led by the Session Chair and a Session Poster Chair who will together be responsible for incorporating the posters participants into the discussion. In the ninth, and last, session prominent participants will summarize sections of the conference in relation to where the field has been and may go in the next millennium.